As a position detection apparatus, encoder apparatuses as disclosed in, for example, the following patent documents are known.    Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H05-133768    Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H05-118873
Encoder apparatuses use a detector to detect a scale member on which a scale is arranged. If a surface state of the scale member is deteriorated by, for example, foreign matter being attached to the surface of the scale member, there is a possibility that a detection failure will occur.
Aspects of the present invention have an object to provide an encoder apparatus capable of suppressing an occurrence of a detection failure.